FIGS. 1-2 depict a prior art locking device 10 for an injection molding machine (not shown) having upper and lower mold plates 11, 12, respectively. Locking device 10 includes a base 40 having a longitudinal axis 72 and a vertical axis 74. Base 40 is attached to lower mold plate 12. This is accomplished via socket head cap screws 60; 61 which fit inside countersunk clearance holes 46, 47 of the base. The cap screws are then tightened appropriately. To assist with proper location of the base on the lower mold plate, locating pins 62, 63, projecting away from back surface 43, are mounted to the base. During installation of the base, locating pins 62, 63 are received by corresponding blind holes (not shown) in the lower mold plate. Base 40 has hole 52 extending therethrough which is substantially parallel to longitudinal axis L. Hole 52 is at least partially threaded, as shown at 53.
Internal slots 54, 55 (having inner limits 58, 59 and outer limits 56, 57, respectively) are proximate end of hole 52 and guide the axial displacement of cylindrical elements 64, 65 substantially parallel to the longitudinal axis during movement of rectangular projection 30 of block 20 into and out of rectangular opening 50 (as explained further below). Internal slots 54, 55 are aligned with hole 52, and furthermore intersect both hole 52 (end of hole 52) and rectangular opening 50.
Rectangular opening 50 is substantially parallel to vertical axis 74, and has a chamfered surface 51. Holes 48, 49 in front surface 42 of the base are used for installing cylindrical elements 64, 65 into the internal slots of the base. Biasing elements 66, 67 are within hole 52, captured between elements 64, 65 and adjustment screws 70, 71, respectively. Lock nuts 68, 69 keep adjustment screws 70, 71 from loosening during operation of the injection molding machine in order to maintain a force on the cylindrical elements that is directed towards vertical axis 74.
Block 20 is attached to upper mold plate 11. This is accomplished via socket head cap screws 27, 28 which fit inside countersunk clearance holes 24, 25 of the block. The cap screws are then tightened appropriately. To assist with proper location of the block on the upper mold plate, a locating pin 29 projecting away from back surface 23 is mounted within through hole 26 of the block. During installation of the block, locating pin 29 is received by a corresponding blind hole (not shown) in the upper mold plate. Block 20 has a rectangular projection 30 which extends perpendicularly away from lower surface 21 and fits into rectangular opening 50 of the base when locking device 10 is in a locked position (not shown). Rectangular projection 30 has a projection longitudinal axis 73. Together, upper and lower mold plates 11, 12 form a mold. In the locked position, the upper and lower mold plates are substantially in contact due to the injection molding machine's closing of the mold. The upper and lower mold plates remain in contact until a selected point of the injection molding cycle is reached when it is desirable to eject the molded part. Prior to or simultaneously with ejection, the die lock releases one mold plate from the other so that displacement of oen plate relative to the other and ejection may occur. When the selected point is reached, a “hard stop” in the die assembly is encountered (at a selected displacement of the mold plates). Here, the force created as the mold plates begin to separate and rectangular projection 30 begins to retract from base 40 causes the spring-loaded cylindrical elements to separate from pair of semicircular features 32 of rectangular projection 30, which unlocks the device. The rectangular projection is then withdrawn from the rectangular opening of the base by the continuing motion of the upper plate away from the lower plate.